Alkenyl-substituted succinic anhydrides have been used as dispersants. Such alkenyl-substituted succinic anhydrides have been prepared by various processes, including a thermal process (see, e.g., U.S. Pat. No. 3,361,673) and a chlorination process (see, e.g., U.S. Pat. No. 3,172,892). The polyisobutenyl succinic anhydride ("PIBSA") produced by the thermal process has been characterized as a monomer containing a double bond in the product. Although the exact structure of chlorination PIBSA has not been definitively determined, the chlorination process PIBSAs have been characterized as monomers containing either a double bond, a ring, other than a succinic anhydride ring and/or chlorine in the product. [See J. Weill and B. Sillion, "Reaction of Chlorinated Polyisobutene with Maleic Anhydride: Mechanism Catalysis by Dichloromaleic Anhydride," Revue de I 'Institut Francais du Petrole, Vol. 40, No. 1, pp. 77-89 (January-February, 1985).] Such compositions include one-to-one monomeric adducts (see, e.g., U.S. Pat. Nos. 3,219,666; 3,381,022) as well as adducts having polyalkenyl-derived substituents adducted with at least 1.3 succinic groups per polyalkenyl-derived substituent (see, e.g., U.S. Pat. No. 4,234,435).
In addition, copolymers of maleic anhydrides and some aliphatic alpha-olefins have been prepared. The polymers so produced were useful for a variety of purposes, including dispersants for pigments and intermediates in the preparation of polyesters by their reaction with polyols or polyepoxides. However, olefins having more than about 30 carbon atoms were found to be relatively unreactive. (See, e.g., U.S. Pat. Nos. 3,461,108; 3,560,455; 3,560,456; 3,560,457; 3,580,893; 3,706,704; 3,729,450; and 3,729,451).
U.S. Pat. No. 5,112,507 shows copolymers of unsaturated acidic reactants and high molecular weight olefins that are useful as dispersants in lubricating oils and fuels and as intermediates in the preparation of polysuccinimide additives that give excellent deposit control. The ratio of anhydride groups to the hydrocarbon groups in those copolymers is generally 1.0.